I don't disagree about what WotC hasn't done. But I also don't know if I agree that it's something WotC should need to do. Ceding certain things to 3PPs and internet GMs is how I personally think a lot of things could and should probably go.5e more or less didn't give DMs seriously designed optional or variant rules for tables who did want more complex or gamey skill play in their DMG. And 10 years later, still doesn't and ceded that to 3PPs and internet GM posters. Not like they wouldn't sell either. Good skills options might have boosted book sales by a lot.
As far boosting sales by having more skill options? That's a statement that neither side would ever be able to prove one way or the other, so I'm not even going to try and speculate. I would most certainly just be talking about my rear end.